(1) Field of the Invention
This invention relates to a phosphor slurry composition for color Braun tubes, more particularly, to a phosphor slurry composition comprising an aqueous ethyl silicate solution and an aqueous zinc sulfate solution in addition to the ingredients of the conventional phosphor slurry composition and usable to manufacture color Braun tubes exhibiting significantly increased luminescent brightness.
(2) Description of the Prior Art
In general, the inner face of a color Braun tube is provided with a fluorescent screen which contains red phosphor, blue phosphor and green phosphor uniformly deposited thereon. As a method to form such a fluorescent screen, the slurry method is widely used. In this method, a procedure of coating a phosphor slurry composition containing a photoresist material on the inner face of a color Braun tube to form a photoresist film, and carrying out the developing process by exposure to light through a shadowmask is sequentially carried out as to green phosphor, blue phosphor and red phosphor, thereby a fluorescent screen is formed.
As an example of the phosphor slurry composition used in the slurry method, a phosphor slurry consisting of phosphor powder, polyvinyl alcohol, sodium hexametaphosphate, sodium dichromate and deionized water is disclosed in Japanese Patent No. Sho 59-19156.
The fluorescent screens produced by using the conventional phosphor slurry compositions have a low packing density of phosphor layer and poor evenness so that the mirror reflection effect of the aluminum vacuum evaporation film will be insufficient, leading to a decrease of luminescent brightness of the fluorescent screens.
Besides the slurry method, the phosphor powder coating method is another method to produce a phosphor coating. This method is disclosed by way of example in Japanese Patent Publication No. Sho 57-20651.
According to this method, when phosphors are coated over the surface of the panel in the shape of fine dots or stripes as in the case of color Braun tubes, parts of the phosphor dots or stripes with the second and/or third color peel off or fail to be deposited to a sufficient thickness, leading to a problem that the obtained fluorescent screen has low grade quality. To solve this problem, in Japanese patent laid-open No. Sho. 62-110230 is disclosed a method which further comprises a step to heat the photosensitive adhesive film prior to the step to deposit each phosphor powders.
However, this method has a defect that a large quantity of heat energy is consumed and the processes get more complicated.